This invention relates to ultraviolet light absorbing polymer compositions, and more particularly, to polymer compositions comprising copolymers of 2-(2'-hydroxy-5'-acryloyloxyalkoxy phenyl)-2H-benzotriazole with one or more other monomers copolymerizable therewith, particularly acrylic monomers. This invention further relates to ocular devices, particularly intraocular lenses and contact lenses, prepared from such ultraviolet light absorbing polymers.
The absorption of radiation in the ultraviolet range by polymeric materials is a major cause of the light-induced degradation therein. It is standard practice to add a low molecular weight UV "stabilizer" to light-sensitive polymers to absorb the light in the destructive range or to quench the energy generated as a result of the excitation of the light-absorbing functional groups in the polymer.
Although low molecular weight UV absorbers or quenchers of various types are effective in inhibiting or retarding the destruction of the polymers to which they are added, their extractibility in various media and/or their volatility during the processing or fabrication of the polymers at elevated temperatures place a limitation on their utility.
This problem has been remedied to a considerable extent by the synthesis of copolymerizable monomers containing structural moieties capable of function as UV absorbers or quenchers. The copolymerization of such monomers results in the formation of copolymers with increased stability, i.e., resistance to degradation upon exposure to UV light with decreased extractibility and volatility. The addition of such polymers to a suitable matrix polymer imparts these properties to the latter.
U.S. Pat. No. 4,304,895 discloses the use of 2-hydroxy-4-methacryloyloxybenzophenone and mixtures thereof as a monomeric ultraviolet light absorber copolymerizable with acrylic monomers and useful in the preparation of UV absorbing hard contact lenses.
Similarly, the copolymerization of an allyl-2-hydroxy-benzophenone with an acrylate ester such as methyl methacrylate is described in U.S. Pat. No. 4,310,650, and, the copolymerization of ethylenically unsaturated derivatives of 2,4-dihydroxy benzophenone with other vinyl type comonomers is broadly disclosed in U.S. Pat. No. 3,162,676.
U.S. Pat. No. 4,528,311 discloses cerain benzotriazole monomers which are copolymerizable with vinyl monomers such as methyl methacrylate to yield optically clear polymers useful in the preparation of intraocular and contact lenses. Representative of the disclosed benzotriazole monomers and a particularly preferred compound is 2-(2'-hydroxy-5'-methacryloyloxypropyl-3'-tert-butylphenyl)-5-chloro-2H-be nzotriazole which has the structure ##STR1##
UV absorbing lenses are particularly desirable for use by persons who have had their natural lenses surgically removed due to cataracts or other deterioration of the lens. The visual correction of aphakia resulting from such lens removal requires the use of high plus corrective lens which may be in the form of spectacles, contact lens or intraocular lens.
In the normal eye, a portion of incident light entering the eye is absorbed by various parts of the eye so that only the unabsorbed or transmitted portion strikes the retina. Incident light may comprise the entire spectrum of wavelengths including the ultraviolet, visible and infrared.
The cornea preferentially absorbs the ultraviolet portion of the light with wavelengths up to about 300 nm. The crystalline lens preferentially absorbs ultraviolet light with wavelengths from about 300 up to about 400 nm. The crystalline lens also absorbs a significant portion of the visible light at wavelengths of from 400 to about 450 nm, particularly as the lens ages and develops a yellow tint. In the aphakic eye, where there is no crystalline lens, light from 300 to 450 nm will be transmitted directly to the retina, and the total spectrum of the light striking the retina in the aphakic eye will be different from that in the normal eye. As a consequence, aphakic patients are very sensitive to light in the ultraviolet range and may experience discomfort or color confusion when exposed to natural light or artificial light having high levels of ultraviolet wavelengths.
Intraocular lenses and hard contact lenses are presently produced from methylmethacrylate polymers which exhibit a combination of properties desirable for such products, particularly optical clarity, the capability of being cut and polished to specific optical powers, and chemical inertness. Soft contact and intraocular lenses may be fabricated of silicone or fluorocarbon polymers, or hydrogels such as hydroxymethyl methacrylate and N-vinylpyrrolidone. UV absorbing lenses of polymethylmethacrylate (PMMA) are required to maintain these properties while achieving at least 85% absorption of light to 400 nm based on a polymer film thickness of 1 mm. In addition, absorption should be minimal above 450 nm to avoid excessive yellowing of the lens.
While the benzotriazole monomers described in U.S. Pat. No. 4,528,311 are effective UV absorbers and form chemically stable copolymers with, for example, methyl methacrylate, a concentration of about 3 percent of the monomer in the copolymer is required to provide the desired degree of absorption to 400 nm. The absorption of such copolymers cuts off sharply above 400 nm so that very little light in the 400 to 450 nm range is absorbed. As a consequence, lenses of PMMA copolymers do not demonstrate the same absorption characteristics as the natural lens of an elderly person who is the most frequenct recipient of an intraocular lens.
It is accordingly an object of the present invention to provide a copolymer composition with improved UV absorption characteristics. It is a further object to provide a novel UV absorbing monomer material which is copolymerizable with vinyl and silicone monomers. A yet further object is to provide a new composition of matter which, when copolymerized at low concentrations with other monomers, effectively absorbs at least 85% of incident light below 420 nm at 1 mm thickness. It is a further object to provide a new monomeric material which absorbs UV light in the range of 300 to 400 nm more effectively than prior art materials. These and other objects of the present invention will be apparent from the ensuing description and claims.